1. Field of the Invention
The present invention relates to the control and management of a virtual computer system.
2. Description of the Related Art
In these years, a technology is drawing attention where resources on a single computer are divided into multiple virtual computers and where a system comprising the multiple computers is integrated in a small number of physical computers. By reducing the number of physical computers, the reduction in power consumption and the simplification of management, thus, the reduction in operational costs can be achieved.
While the control technology for these virtual computers is drawing attention in these years because of advance in support techniques for constructing a virtual computer system using inexpensive computers of a PC (Personal Computer) architecture or the like, the control technology has been realized mainly in the control of main frames (general-purpose large-scale computers) or the like.
For such virtual computer systems, there are two schemes for controlling devices such as a network interface card (NIC) and a SCSI (Small Computer System Interface) card on computers. Hereinafter, devices actually mounted on computers are called physical devices, and devices recognized by virtual computers are called virtual devices.
A first one of the schemes is a scheme where a hypervisor that is the control unit (managing unit) of a virtual computer detects and analyzes control commands, issued to a virtual device from one or a number of virtual computers to emulate the operation of a physical device. With this scheme, overhead associated with the hypervisor is large and processing performance is degraded, while multiple virtual computers can share a single physical device. Further, where multiple virtual computers share a single physical device, there are the problems that it is difficult to secure processing performance, e.g., when multiple virtual computers use the physical device at the same time and that the performance prediction is difficult. Hereinafter, this first scheme is called a shared scheme.
A second scheme is a scheme where a hypervisor manages association between a particular physical device and a virtual computer and performs only the division of computer resources and where the virtual computer directly controls the physical device. Hereinafter, the second scheme is called a dedicated scheme. With the dedicated scheme, operation is at high speed, but physical devices cannot be shared.
Described in U.S. Pat. No. 4,887,202 (hereinafter called a reference 1) is a method that changes the scheme of controlling virtual devices from the shared scheme to the dedicated scheme, or from the dedicated scheme to the shared scheme in a virtual computer system having the two schemes.
Described in U.S. Pat. No. 6,725,289 (hereinafter called a reference 2) is a method that monitors the usage of virtual devices under the shared scheme and optimizes a page table of memory.
If in a practical system, all virtual devices are configured for the dedicated scheme, the number of physical devices that are to be mounted in computers increases. However, since there is a limit to the number of physical devices mountable in computers, it is difficult to configure all virtual devices in the dedicated scheme.
Accordingly, it is important to configure a system where the shared scheme and the dedicated scheme are mixed.
In some systems, depending on the usage of virtual devices, the shared scheme may be enough in performance, or the dedicated scheme may be needed in performance. Further, the usage of virtual devices may vary during operation. In particular, in order to secure stable processing performance in a system that varies in the usage, it is important to immediately change the scheme according to the usage.
Further, whether a virtual device operating under the shared scheme can be changed to operate under the dedicated scheme, or whether the opposite is possible depends on information about physical devices mounted in the system, the settings of virtual devices and the physical devices, and the like. For example, when a virtual device under the shared scheme is changed to operate under the dedicated scheme, in a general architecture such as PC/AT (Personal Computer/Advanced Technology), an identifier such as the mounted position of the virtual device needs to be the same.
Although reference 1 describes a method of changing the control scheme for virtual devices, because information about the system configuration and the usage of the virtual devices are not managed, time to change the control scheme and the control scheme to be used cannot be automatically determined. Hence, an instruction to change must be given externally.
Also in reference 2, the control scheme to be used cannot be automatically determined.
If a human manually performs that change, management cost will increase proportionally to the number of computers, thus resulting in large management cost. Moreover, if manual work time is necessary, the scheme in use cannot be switched quickly. Thus, degradation in performance for a long time may be caused. Hence, a method of changing the control scheme at high speed without manual intervention is needed.
Accordingly, a method of managing information about both the usage of virtual devices and the system configuration collectively and determining time to change the control scheme and the control scheme to be used is needed.